Doom (typeset as DOOM in official documents)[1] is a 1993 science fiction horror-themed first-person shooter (FPS) video game by id Software. It is considered one of the most significant and influential titles in video game history, for having helped to pioneer the now-ubiquitous first-person shooter. The original game was divided into three nine-level episodes and was distributed via shareware and mail order. The Ultimate Doom, an updated release of the original game featuring a fourth episode, was released in 1995 and sold at retail.

In Doom, players assume the role of an unnamed space marine, who became popularly known as "Doomguy"[2], fighting his way through hordes of invading demons from Hell.[3] With one-third of the game (nine levels) distributed as shareware, Doom was played by an estimated 15–20 million people[4] within two years of its release, popularizing both the business model of online distribution[5] and the mode of gameplay, and spawning a gaming subculture. In addition to popularizing the FPS genre, it pioneered immersive 3D graphics, networked multiplayer gaming, and support for customized additions and modifications via packaged files in a data archive known as "WADs". As a sign of its effect on the industry, first-person shooter games from the genre's boom in the 1990s, helped in no small part by the game's release, became known simply as "Doom clones". Its graphic violence, as well as satanic imagery, made Doom the subject of considerable controversy.

The Doom franchise was later continued with the follow-up Doom II: Hell on Earth (1994) and numerous expansion packs, including Master Levels for Doom II (1995), and Final Doom (1996). Originally released for MS-DOS, the games have been ported to numerous other platforms. Once the game's source code was released in 1997, it spawned even more adaptations, as fans further ported the code to countless devices. The series started to lose mainstream appeal as the technology of the Doom game engine was surpassed in the mid-1990s, although fans have continued making Wads, speedruns, and modifications to the original. The franchise again received popular attention in 2004 with the release of Doom 3, a retelling of the original game using id Tech 4, with an associated 2005 Doom motion picture. Another release, simply titled Doom and powered by id Tech 6, was released in 2016 and focused on returning to the fast paced action of the first two games.

The unnamed protagonist of the Doom series as he appears in The Ultimate Doom.

Doom, a science fiction/horror themed video game, has a background which is given in the game's instruction manual; the rest of the story is advanced with short messages displayed between each section of the game (called episodes), the action as the player character progresses through the levels, and some visual cues.

The player takes the role of an unnamed space marine ("Doomguy") who has been punitively posted to Mars after assaulting his commanding officer, who ordered his unit to fire on civilians. The Martian space marine base acts as security for the Union Aerospace Corporation, a multi-planetary conglomerate, which is performing secret experiments with teleportation by creating gateways between the two moons of Mars, Phobos and Deimos. Mars is considered by space marines to be the dullest assignment imaginable. This all changes when the UAC experiments go horribly wrong. Computer systems on Phobos malfunction, Deimos disappears entirely, and "something fragging evil" starts pouring out of the gateway, killing or possessing all UAC personnel. Responding to a frantic distress call from the overrun scientists, the Martian marine unit is quickly sent by ship from Mars to Phobos to investigate, where the player character is left to guard the perimeter with only a pistol while the rest of the group proceeds inside. The marine hears assorted radio messages, gunfire, and screams, followed by silence: "Seems your buddies are dead." The player cannot navigate the ship off of Phobos alone and sees that the only way out is to fight through the Phobos complex.

As the last man standing, the player character's mission is to fight through the entire onslaught of demonic enemies by himself in order to keep them from attacking Earth. Knee-Deep in the Dead, the first episode and the only one in the shareware version, is set in the high-tech military bases, power plants, computer centers and geological anomalies on Phobos. It ends with the player character entering the teleporter leading to Deimos, only to be overwhelmed by monsters. In the second episode, The Shores of Hell, the marine has successfully teleported to Deimos. He fights his way through installations on Deimos, similar to those on Phobos, but warped and distorted from the demon invasion and interwoven with beastly architecture. After defeating the titanic Cyberdemon, the marine discovers the truth about the vanished moon: it is floating above Hell. The third episode, called Inferno, begins after the marine climbs off Deimos to the surface. The marine fights his way through Hell and defeats the Spider Mastermind that planned the invasion. Then a hidden doorway back to Earth opens for the hero, who has "proven too tough for Hell to contain". However, a burning city and a rabbit's head impaled on a stake (named in The Ultimate Doom as the marine's pet rabbit, Daisy) show that the demons have invaded Earth, setting the stage for Hell on Earth. In The Ultimate Doom expansion, in the fourth episode Thy Flesh Consumed, it tells that the marine fought valiantly against the hordes of demons that the Spider Mastermind sent through that hidden doorway but ultimately the forces of Hell prevailed in the invasion of Earth. The locales of Thy Flesh Consumed are varied, including a mix of high-tech bases and demonic temples, though the atmosphere appears to be Earth.

"Episode I: Knee-Deep in the Dead" takes place in the research, industrial and military facilities on the surface of Phobos. In the screenshot, the player armed with a chainsaw confronts a basic zombie marine on a bridge over a chemical waste storage

Being a first-person shooter, Doom is experienced through the eyes of the main character. This character is not named throughout the game. The game's designer, John Romero, has pointed out that this is so the player feels more involved in the game: "There was never a name for the DOOM marine because it's supposed to be you."[6] At its core, the gameplay is similar to classic shooter games, presenting the player with the challenge of surviving while shooting every enemy in sight, but with its pseudo-3Dfirst-person perspective giving environments a spatial representation that has a major effect on the level design and gameplay experience.[7]

In order for the game to be completed, the marine must fight through Phobos, Deimos, and then Hell itself, each presented as an episode containing eight distinct levels, along with an optional ninth hidden level for each one. The Ultimate Doom, the retail store version of the game, adds a fourth episode, Thy Flesh Consumed. Set between the end of Doom and before Doom II and featuring the first contribution of Tim Willits to the Doom franchise, the fourth episode was designed for expert Doom players seeking a major challenge (being considerably more difficult than the original episodes).

The objective of each level is simply to locate the exit room that leads to the next area, marked with an exit sign and/or a special kind of door, while surviving all hazards on the way. Among the obstacles are demonic monsters, pits of toxic or radioactive slime, ceilings that lower and crush anything below them, and locked doors which require a keycard, skull-shaped key device, or a remote switch to be located. The levels are sometimes labyrinthine and feature plenty of items such as additional ammo, health increases and other "power-ups" along the way, as well as the occasional secret areas which are not immediately obvious as a reward for players who explore more carefully. To ease navigation through the levels, a full screen automap is available and shows the areas explored to that point. Many versions of Doom (and its sequels) include secret levels which are accessed by the player discovering alternate exits, often hidden behind secret doors, hidden passageways, or in areas which are difficult to reach. Despite carrying masses of high-tech weaponry, the main character can still run at blistering speeds.

Doom is notable for the weapons arsenal available to the marine, which became prototypical for first-person shooters. The player character starts armed only with a pistol, and fists in case the ammunition runs out, but larger weapons can be picked up: these are a chainsaw, a shotgun, a chaingun, a rocket launcher, a plasma rifle, and finally the immensely powerful BFG 9000. There is a wide array of power-ups, such as a backpack that increases the player character's ammunition-carrying capacity, armor, first aid kits to restore health, the berserk pack which both restores health and causes the player's punching attack to deal enormous damage, supernatural blue orbs (named soul spheres in the manuals) that boost the player character's health up to a maximum of 200%, nightvision, computer maps (which show every area of the level), partial invisibility, and protective suits that allow the player to survive in toxic acids.

The enemy monsters in Doom make up the central gameplay element. The player character faces them in large numbers, with the number generally increased when the higher of the game's five difficulty levels is chosen when starting a new game. There are ten types of monsters, including possessed undead humans as well as demons, all which vary in many ways. The monsters have very simple behavior, consisting of either walking toward their opponent, or attacking by throwing fireballs, biting, and scratching. They will fight each other if one monster is accidentally harmed by another (though most monsters are not harmed by the ranged attacks of their own kind).

Doom contains some cheat codes that allow the player to be invulnerable, obtain every weapon, be able to instantly kill every monster in a particular level, and several other abilities. Two of the best-known cheats were "all weapons and keys" cheat ("IDKFA") and God mode ("IDDQD").[9][10][11][12]

Designer Tom Hall wrote an elaborate design document called the Doom Bible, according to which the game would feature a detailed storyline, multiple player characters, and a number of interactive features.[17] However, many of his ideas were discarded during development in favor of simpler design primarily advocated by John Carmack, resulting in Hall in the end being forced to resign due to not contributing effectively in the direction the rest of the team was going. Most of the level design that ended up in the final game is that of John Romero and Sandy Petersen. The graphics, by Adrian Carmack, Kevin Cloud and Gregor Punchatz, were modelled in various ways: although much was drawn or painted, several of the monsters were built from sculptures in clay or latex, and some of the weapons are toy guns from Toys "R" Us. A heavy metal-ambient soundtrack was supplied by Bobby Prince.[8]

Doom's primary distinguishing feature at the time of its release was its relatively realistic 3D graphics.[18] The advance from id Software's previous game Wolfenstein 3D was enabled by several new features in the Doom engine, including height differences (all rooms in Wolfenstein 3D have the same height), full texture mapping of all surfaces (in Wolfenstein 3D, floors and ceilings are flat colors) and varying light levels and custom palettes (all areas in Wolfenstein 3D are fully lit at the same brightness). The latter contributed to Doom's visual authenticity, atmosphere and gameplay, as the use of darkness to frighten or confuse the player was nearly unheard of in games released prior to Doom; palette modifications were used to enhance effects such as the berserk power-up which tints the player's vision red.

In contrast to the static levels of Wolfenstein 3D, those in Doom are highly dynamic: platforms can lower and rise, floors can rise sequentially to form staircases, and bridges can rise and fall. The immersive environments were enhanced further by the stereo sound system, which made it possible to roughly determine the direction and distance of a sound effect. The player is kept on guard by the grunts and growls of monsters, and receives occasional clues to finding secret areas in the form of sounds of hidden doors opening remotely. As in Wolfenstein 3D, enemies can also become aware of the player's presence by hearing distant gunshots.

John Carmack had to make use of several tricks for these features to run smoothly on home computers of 1993. Most significantly, the Doom engine and levels are not truly three-dimensional; they are internally represented on a single plane, with height differences stored separately as displacements (a similar technique is still used in many games to create expansive outdoor environments). This allows a two-point perspective projection, with several design limitations: for example, it is not possible in the Doom engine to create one room over another room in a level. However, thanks to its two-dimensional property, the environment can be rendered very quickly, using a binary space partitioning method. Another benefit was the clarity of the automap, as that could be rendered with 2D vectors without any risk of overlapping. Additionally, the BSP tree technology created by Bruce Naylor was used.[19]

Another important feature of the Doom engine is its modular data files, which allow most of the game's content to be replaced by loading custom WAD files. Wolfenstein 3D was not designed to be expandable, but fans had nevertheless figured out how to create their own levels for it, and Doom was designed to further extend the possibilities. The ability to create custom scenarios contributed significantly to the game's popularity (see the section on WADs, below).

The development of Doom was surrounded by much anticipation.[20] The large number of posts in Internet newsgroups about Doom led to the SPISPOPD joke,[21] to which a nod was given in the game in the form of a cheat code. In addition to news, rumors and screenshots, unauthorized leaked alpha versions also circulated online. Many years later these alpha versions were sanctioned by id Software because of historical interest; they reveal how the game progressed from its early design stages.[22] The first public version of Doom was uploaded to Software Creations BBS and an FTP server at the University of Wisconsin–Madison on December 10, 1993.[23] Anticipation over the release was so great that the Wisconsin FTP site hit its maximum of 125 simultaneous users, preventing id's Jay Wilbur from uploading the game. The system administrator raised the limit by 50 users but others also quickly logged on and Wilbur was barely able to do so in time. Hundreds of others watched the upload process on an IRC channel; when the upload was complete thousands connected to the Wisconsin site at once, crashing it twice.[20]

Doom was released as shareware, with people encouraged to distribute it further. id liked the distribution method because of high profit margins from not having marketing or retail costs, and it could quickly release games to the public.[20] Although most users did not purchase the registered version, over one million copies have been sold, and the popularity helped the sales of later games in the Doom series that were not released as shareware. In 1995, The Ultimate Doom (version 1.9, including Episode IV) was released, making this the first time that Doom was sold commercially in stores.

In a press release dated January 1, 1993, id Software had written that they expected Doom to be "the number one cause of decreased productivity in businesses around the world."[24] This prediction came true at least in part: Doom became a major problem at workplaces, both occupying the time of employees and clogging computer networks with traffic caused by deathmatches. Intel,[25]Lotus Development, and Carnegie Mellon University were among many organizations reported to form policies specifically disallowing Doom-playing during work hours. At the Microsoft campus, Doom was by one account equal to a "religious phenomenon".[8] Doom was #1 on Computer Gaming World's "Playing Lately?" survey for February 1994. One reader said that "No other game even compares to the addictiveness of NetDoom with four devious players! ... The only game I've stayed up 72+ straight hours to play", while another reported that "Linking four people together for a game of Doom is the quickest way to destroy a productive, boring evening of work".[26]

In late 1995, Doom was estimated to be installed on more computers worldwide than Microsoft's new operating system Windows 95, despite million-dollar advertising campaigns for the latter.[27] The game's popularity caused Microsoft to hire id Software to port Doom to Windows with the WinG API,[28] and Bill Gates briefly consider buying the company.[8] Microsoft developed a Windows 95 port of Doom to promote the operating system as a gaming platform. The development team in this effort was led by then-employee Gabe Newell.[27] One Windows 95 promotional video had Bill Gates digitally superimposed into the game.[29] The 1995 release of Microsoft Excel 95 included a Doom-esque secret level as an Easter egg containing portraits of the programmers among other things.[30]

Software was written for net servers designed to detect and stop Doom-related inter-player messages.

The game was made available on Steam on August 3, 2007, running on the DOSBox DOS emulator.[31]

The ability for others to create custom levels and otherwise modify the game, in the form of custom WAD files (short for "Where's All the Data?"),[34] turned out to be a particularly popular aspect of Doom. Gaining the first large mod-making community, Doom affected the culture surrounding first-person shooters, and also the industry. Several future professional game designers started their careers making Doom WADs as a hobby, among them Tim Willits, who later became the lead designer at id Software.

The first level editors appeared in early 1994, and additional tools have been created that allow most aspects of the game to be edited. Although the majority of WADs contain one or several custom levels mostly in the style of the original game, others implement new monsters and other resources, and heavily alter the gameplay; several popular movies, television series, other video games and other brands from popular culture have been turned into Doom WADs by fans, including Aliens, Star Wars, The Simpsons, South Park, Sailor Moon, Dragon Ball Z, Pokémon, Beavis and Butt-head, Batman, and Sonic the Hedgehog.[35] Some works, like the Theme Doom Patch, combined enemies from several films, such as Aliens, Predator, and The Terminator. Some add-on files were also made that changed the sounds made by the various characters and weapons.

Around 1994 and 1995, WADs were primarily distributed online over bulletin board systems or sold in collections on compact discs in computer shops, sometimes bundled with editing guide books. FTP servers became the primary method in later years. A few WADs have been released commercially, including the Master Levels for Doom II, which was released in 1995 along with Maximum Doom, a CD containing 1,830 WADs that had been downloaded from the Internet. Several thousand WADs have been created in total: the idgames FTP archive contains over 18,000 files,[36] and this represents only a fraction of the complete output of Doom fans. Third party programs were also written to handle the loading of various WADs, since the game is a DOS game and all commands had to be entered on the command line to run. A typical launcher would allow the player to select which files to load from a menu, making it much easier to start. In 1995, WizardWorks released the D!Zone pack featuring hundreds of levels for Doom and Doom II.[37]D!Zone was reviewed in Dragon by Jay & Dee; Jay gave the pack 1 out of 5 stars, while Dee gave the pack 1½ stars.[37]

Doom received critical acclaim and was widely praised in the gaming press, broadly considered to be one of the most important and influential titles in gaming history. Upon release, GamesMaster gave it a 90% rating.[38]Dragon gave it five stars, praising the improvements over Wolfenstein 3D, the "fast-moving arcadeshoot 'em up" gameplay, and network play.[40] A common criticism of Doom was that it was not a true 3D game, since the game engine did not allow corridors and rooms to be stacked on top of one another (room-over-room), and instead relied on graphical trickery to make it appear that the player character and enemies were moving along differing elevations.[55]

Computer Gaming World stated in February 1994 that Wolfenstein 3D fans should "look forward to a delight of insomnia", and "Since networking is supported, bring along a friend to share in the visceral delights".[56] A longer review in March 1994 said that Doom "was worth the wait ... a wonderfully involved and engaging game", and its technology "a new benchmark" for the gaming industry. The reviewer praised the "simply dazzling" graphics", and reported that "DeathMatches may be the most intense gaming experience available today". While criticizing the "ho-hum endgame" with a too-easy end boss, he concluded that "DOOM is a virtuoso performance".[57]Edge gave it a 7/10 rating, criticizing the "fairly simple 3D perspective maze adventure/shoot 'em up" gameplay but praising the graphics and levels.[41]

In 1994, PC Gamer UK named Doom the third best computer game of all time. The editors wrote, "Although it's only been around for a couple of months, Doom has already done more to establish the PC's arcade clout than any other title in gaming history."[54] In 1994 Computer Gaming World named Doom Game of the Year.[42] In 1996 the magazine ranked it as the fifth best video game of all time,[43] and the third most-innovative game.[44] In 1995, Next Generation said it was "The most talked about PC game ever – and with good reason. Running on a 486 machine (essential for maximum effect), Doom took PC graphics to a totally new level of speed, detail, and realism, and provided a genuinely scary degree of immersion in the gameworld."[58] In 2001, Doom was voted the number one game of all time in a poll among over 100 game developers and journalists conducted by GameSpy.[45] In 2003, IGN ranked it as the 44th top video game of all time and also called it "the breakthrough game of 1993", adding: "Its arsenal of powerful guns (namely the shotgun and BFG), intense level of gore and perfect balance of adrenaline-soaked action and exploration kept this gamer riveted for years."[46]PC Gamer proclaimed Doom the most influential game of all time in its ten-year anniversary issue in April 2004. In 2004, readers of Retro Gamer voted Doom as the ninth top retro game, with the editors commenting: "Only a handful of games can claim that they’ve changed the gaming world, and Doom is perhaps the most qualified of them all."[59] In 2005, IGN ranked it as the 39th top game.[47] On March 12, 2007, The New York Times reported that Doom was named to a list of the ten most important video games of all time, the so called game canon.[60] The Library of Congress took up this video game preservation proposal and began with the games from this list.[49][61] In 2009, GameTrailers ranked Doom as number one "breakthrough PC game".[50] That year Game Informer put Doom sixth on the magazine's list of the games of all time, stating that it gave "the genre the kick start it needed to rule the gaming landscape two decades later."[51]Game Informer staff also put it sixth on their 2001 list of the 100 best games ever.[62] IGN included Doom at 2nd place in the Top 100 Video Game Shooters of all Time, just behind Half-Life, citing the game's "feel of running and gunning", memorable weapons and enemies, pure and simple fun and its spreading on nearly every gaming platform in existence.[48] In 2012, Time named it one of the 100 greatest video games of all time as "it established the look and feel of later shooters as surely as XeroxPARC established the rules of the virtual desktop," adding that "its impact also owes a lot to the gonzo horror sensibility of its designers, including John Romero, who showed a bracing lack of restraint in their deployment of gore and Satanic iconography."[52] Including Doom on the list of the greatest games of all time, GameSpot wrote that "despite its numerous appearances in other formats and on other media, longtime fans will forever remember the original 1993 release of Doom as the beginning of a true revolution in action gaming."[53]

With the release of Doom, id Software, quickly found itself making $100,000 daily with copies sold at $9.[66] Experts estimate that the game sold approximately 2-3 million physical copies from its release through 1999, but it was actually played by 10–20 million people within 24 months of its launch.[4][66] In the United States, it was the eighth best-selling computer game between 1993 and 1999, with 1.1 million units sold. The Ultimate Doom release was the 20th best-selling game in the United States during this period, selling 788,000 copies.[67]

Doom's high level of graphic violence made the game highly controversial. This screenshot shows the effects of a rocket hitting a group of enemies.

Doom was notorious for its high levels of graphic violence[68] and satanic imagery, which generated controversy from a broad range of groups. Doom for the Genesis 32X was among one of the first video games to be given an M for Mature rating from the Entertainment Software Rating Board due to its violent gore and nature.[69]Yahoo! Games listed it as one of the top ten most controversial games of all time.[70] It was criticized by religious organizations for its diabolic undertones and was dubbed a "mass murder simulator" by critic and Killology Research Group founder David Grossman.[71]Doom prompted fears that the then-emerging virtual reality technology could be used to simulate extremely realistic killing.

The game again sparked controversy throughout a period of school shootings in the United States when it was found that Eric Harris and Dylan Klebold, who committed the Columbine High School massacre on April 20, 1999, were avid players of the game. While planning for the massacre, Harris said in his journal that the killing would be "like playing Doom", and "it'll be like the LA riots, the Oklahoma bombing, World War II, Vietnam, Duke Nukem and Doom all mixed together", and that his shotgun was "straight out of the game".[72] A rumor spread afterwards that Harris had designed a Doom level that looked like the high school, populated with representations of Harris's classmates and teachers, and that Harris practiced for his role in the shootings by playing the level over and over. Although Harris did design Doom levels, which later became known as the 'Harris levels', none have been found to be based on Columbine High School.

The Doom series remained dormant between 1997 and 2000, when Doom 3 would finally be announced. A retelling of the original Doom using entirely new graphics technology and a slower pace survival horror approach, Doom 3 was hyped to provide as large a leap in realism and interactivity as the original game and helped renew interest in the franchise when it was released in 2004, under the id Tech 4 game engine.

The series would again remain dormant for 10 years until a remake, simply titled Doom and running on the new id Tech 6, was announced with a beta access to players that had pre-ordered Wolfenstein: The New Order. The game held its closed alpha multiplayer testing on October 2015, as closed and open beta access ran during March to April 2016. Returning to the series' roots in fast paced action and minimal storytelling, the full game eventually released worldwide on May 13, 2016. The project initially started as Doom 4 in May 2008, set to be a remake of Doom II: Hell on Earth and ditching the survival horror aspect of Doom 3. Development completely restarted as id's Tim Willits remarked that Doom 4 was "lacking the personality of the long-running shooter franchise".[73]

The phrase "Doom clone" was initially popular to describe the style of gameplay in Doom-like games, but was gradually replaced by "first-person shooter" after 1996. By 1998, the phrase "first-person shooter" had firmly superseded "Doom clone".

Doom was influential and dozens of new first-person shooter titles appeared following Doom's release, and they were often referred to as "Doom clones" rather than "first-person shooters". The term "Doom clone" was used to describe the style of gameplay in Doom-like games. While the term was initially popular, it was, after 1996, gradually replaced by "first-person shooter", and the phrase "first-person shooter" had firmly superseded "Doom clone" around 1998. Some of these were certainly "clones", hastily assembled and quickly forgotten, while others explored new grounds of the genre and were highly acclaimed. Many of the games closely imitated features in Doom such as the selection of weapons and cheat codes. Doom's principal rivals were Apogee's Rise of the Triad and Looking Glass Studios' System Shock. The popularity of Star Wars-themed WADs is rumored to have been the factor that prompted LucasArts to create their first-person shooter Dark Forces.[74]

In addition to the thrilling nature of the single-player game, the deathmatch mode was an important factor in the game's popularity. Doom was not the first first-person shooter with a deathmatch mode; Maze War, an FPS released in 1974, was running multiplayer deathmatch over ethernet on Xerox computers by 1977. The widespread distribution of PC systems and the violence in Doom made deathmatching particularly attractive. Two-player multiplayer was possible over a phone line by using a modem, or by linking two PCs with a null-modem cable. Because of its widespread distribution, Doom hence became the game that introduced deathmatching to a large audience and was also the first game to use the term "deathmatch".[76]

Although the popularity of the Doom games dropped with the release of more modern first-person shooters, the game still retains a strong fan base that continues to this day by playing competitively and creating WADs, and Doom-related news is still tracked at multiple websites such as Doomworld. Interest in Doom was renewed in 1997, when the source code for the Doom engine was released (it was also placed under the GNU General Public License on October 3, 1999). Fans then began porting the game to various operating systems, even to previously unsupported platforms such as the Dreamcast. As for the PC, over 50 different Doom source ports have been developed. New features such as OpenGL rendering and scripting allow WADs to alter the gameplay more radically.

Devoted players have spent years creating speedruns for Doom, competing for the quickest completion times and sharing knowledge about routes through the levels and how to exploit bugs in the Doom engine for shortcuts. Achievements include the completion of both Doom and Doom II on the "Ultra-Violence" difficulty setting in less than 30 minutes each. In addition, a few players have also managed to complete Doom II in a single run on the difficulty setting "Nightmare!", on which monsters are more aggressive, launch faster projectiles (or, in the case of the Pinky Demon, simply move faster), and respawn roughly 30 seconds after they have been killed (level designer John Romero characterized the idea of such a run as "[just having to be] impossible").[77] Movies of most of these runs are available from the COMPET-N website.[78]

^Romero, John (5 August 2017). "Doomguy's Identity". DOOM Stories. John Romero's site. Archived from the original on 5 August 2017. Retrieved 10 December 2017. It all started when... Don Punchatz, the illustrator who created the DOOM logo and the famous front box cover art came over to id in mid-1993 with a male body model.

^"The First Pictures". Maximum: The Video Game Magazine. Emap International Limited (1): 134–5. October 1995. Doom was criticised for not being a true 3D product – in fact, it's best described as 2.5D (if you will) because although each level could be staged at various heights, it was impossible to stack two corridors on top of one another in any given stage.